This is mainly just an issue with the legacy bootstrap code that's still used by the Jetpack tests. I guess we should just check whether the module has its own sandbox from JS rather than catching the exception that nukeSandbox throws.

Ick. It looks like those tests bundle pre-built XPIs with ancient versions of the old style bootstrap.js loader. I'm not going to worry about them for now. They should be updated to use the new bootstrap code at some point, though.